What if we were only allotted one grumble per day? You would need to be sure not to use up your one grumble on something that didn't really require it, in case a bigger need for a grumble came later on in the day. Every time you felt yourself starting to grumble you would need to ask yourself “Is this my one grumble today or could I let this one go?”
So if we went with this idea, during the day our question becomes - Does this situation need a grumble, YES or NO ? And you may end up noticing a lot of the NO grumbles really are meaningless. Instead of indulging them with your time and energy, you would likely find you have a lot more time and energy to put towards more meaningful actions.
From there, you could ask yourself, what if I go the whole day and I'm about to go to sleep and I haven't used my one grumble? Do I get to add it to tomorrow? And the answer would be NO, because the less grumbles we carry forward with us the more peaceful our lives become, because now we spend our time focusing on the delights of our day!